This invention relates to a fluid relay apparatus and particularly to a diaphragm-type relay apparatus for controlling one fluid signal from another fluid signal.
In fluid control and operating system, a relatively small fluid control signal controlling a relatively large fluid control or operating signal may be advantageously employed within the system. Fluid relays may be employed as a volume and/or pressure amplifier in which a first fluid pilot signal controls a fluid output signal. In volume amplifiers, a large output fluid volume may be controlled within a given operating pressure range by a small pilot signal. In other applications in which pressure amplification is desired the low pressure pilot signal controls a high pressure output signal. In both applications, either direct or reverse acting response may be required. In typical pneumatic relay device, a multiple diaphragm assembly includes a pilot diaphragm defining a common wall between a pilot chamber and an exhaust chamber. A supply diaphragm forms an opposite wall of the exhaust chamber and a wall of an output chamber. A supply chamber is coupled or extended from the output chamber and interconnected thereto by a suitable spring-loaded valve assembly. A valve assembly also interconnects the exhaust chamber to the output chamber with the exhaust valve seated on the supply valve assembly. In operation, increasing pilot pressure functions to first close the exhaust assembly to the output valve assembly. Further increases in pilot pressure function through the exhaust valve assembly to open the supply valve assembly and connect supply pressure and flow to the output chamber, and therefore to the load or output line. Pressure then increases within the output chamber until balanced by the pilot pressure and a stable output condition is created. If the relay is connected to a dead-ended load, the supply valve closes and the exhaust valve remains closed against the supply valve assembly to hold the pressure just equal to the pilot pressure. Decreasing the pilot pressure first causes the exhaust valve assembly to move from the supply valve for exhausting of air until such time as the equilibrium pressure condition is again established. Increasing of pilot pressure from that position would, of course, again open the supply valve assembly and reestablish an equivalent condition.
Although various modifications of this system are employed, they generally include the separate exhaust chamber having a separate diaphragm connected to control fluid exhaust either through the inter-related cascaded exhaust-supply valve assembly or a separate valved connection in the output system. The spring forces and interrelated fluid forces acting over the various diaphragms in the conventional construction introduce deviations in the system response. Generally, the relays have a significant hysterisis level in the presence of increasing and decreasing input signals. In addition, depending upon the care and special procedure of construction, commercially-produced devices also may have significant deviations from an ideal linear characteristic. For example, a fluid repeater or one to one booster relay desirably has an essentially straight line characteristic with a 1:1 ratio between the input and output pressures and minimal offset, linearity, and hysteresis. Such characteristics might generally be obtained with careful construction and design, but generally require relatively complex and costly apparatus.
There is a need for a relatively simple, and inexpensive booster fluid relay which produces a highly accurate output with minimal offset, hysteresis and deviation from linearity.